Process for producing phenothiazine granules

Abstract

The invention relates to a method for producing a phenothiazine granulate with a narrow particle size distribution. At least 98% pure phenothiazine in liquid form is pressed through a device provided with boreholes and a frequency is applied to said liquid phenothiazine. The liquid phenothiazine discharged through the boreholes enters a cooling medium having a temperature of between −196 and +120° C. The drops of liquid phenothiazine thus produced are brought to a temperature below melting point and are optionally solidified in another post-cooling area. Optionally, fine-grain particles or coarse-grained particles thus formed can be subsequently removed by appropriate methods. The bulk density of the obtained phenothiazine granulates ranges more particularly from 720–780 kg/m 3 .

1. A process for the preparation of phenothiazine granules having a narrow particle size distribution, phenothiazine having a purity of at least 98% in liquid form being forced through a means provided with holes and a frequency being applied to the liquid phenothiazine and the liquid phenothiazine emerging through the holes to form liquid phenothiazine drops and countercurrently contacting said drops with a cooling medium having a temperature in the range of from −40 to +120° C. so that the liquid phenothiazine drops thus produced are brought to a temperature below the melting point of phenothiazine to provide partially crystallized drops and said partially crystallized drops are, if required; further solidified in a downstream cooling zone to provide said phenothiazine granules. 
   
   
     2. The process as claimed in  claim 1 , wherein the means provided with holes is a die plate. 
   
   
     3. The process as claimed in  claim 1 , wherein the cooling medium has a temperature in the range of from −20 to +120° C. 
   
   
     4. The process as claimed in  claim 1 , wherein the cooling medium used is nitrogen or air. 
   
   
     5. The process as claimed in  claim 1 , wherein the cooling medium used is cooled air or cooled inert gas having a temperature in the range of from +20 to +100° C. 
   
   
     6. The process as claimed in  claim 1 , wherein the phenothiazine granules prepared have a particle size distribution in the range of from 300 to 3000 μm, the volume fraction thereof being at least 90%, based on the total volume. 
   
   
     7. The process as claimed in  claim 1 , wherein the phenothiazine granules have a fine particle fraction which is less than 3% of particles <300 μm in size. 
   
   
     8. The process of  claim 1 , wherein the phenothiazine granules have a fine particle fraction which is less than 2% of particles <300 μm in size. 
   
   
     9. The process as claimed in  claim 1 , wherein any fine particle fractions or coarse particle fractions formed are removed by suitable methods. 
   
   
     10. The process as claimed in  claim 1 , wherein a bulk density of the phenothiazine granules obtained is in the range of from 720 to 780 kg/m 3 . 
   
   
     11. The process as claimed in  claim 1 , wherein the phenothiazine granules have a dissolution rate, in acrylic acid, of from 5 to 14 minutes to reach a concentration of 1.5%. 
   
   
     12. A process for the preparation of phenothiazine granules having a narrow particle size distribution, said process comprising:
 a) forcing a molten liquid phenothiazine having a purity of at least 98% through a perforated plate having holes and applying a frequency to said liquid phenothiazine to provide liquid phenothiazine drops emerging through the holes; 
 b) passing the liquid phenothiazine drops to a first cooling zone wherein a cooing medium flowing countercurrently at a velocity of 0.5 to 5 m/s to said drops contacts the liquid phenothiazine drops, said cooling medium having a temperature in the range of from −20 to +100° C. to cool said liquid phenothiazine drops to form phenothiazine granules, wherein at least 95 volume percent of said phenothiazine granules having a particle size distribution in the range of from 500 to 2000 μm, said phenothiazine granules having a dissolution rate in acrylic acid of between 5 to 14 minutes to reach a concentration of 1.5%, and, 
 c) optionally; further cooling said phenothiazine granules in a downstream cooling zone.